It is now customary to provide entire complete enclosures around machines or equipment which emit excessive noise. These enclosures must include barrier walls and ceilings which, when assembled, not only have the necessary sound-absorbing insulating materials incorporated therewithin but also have the necessary structural strength. They ordinarily include expensive insulating materials which are difficult to handle and to incorporate into the walls and which tend to deteriorate with age. The result is that these enclosures are expensive to build and maintain and another of the difficulties of their use is that lighting systems must also be incorporated in the enclosure for observance of the equipment from within the enclosure and still another is that the equipment usually cannot be observed from outside the enclosure without incorporating expensive insulated windows or other observation panels.